Add line_cap parameter

Author: martinRenou

examples/lines.ipynb

@@ -39,12 +39,52 @@
     "canvas"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Line cap"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {},
    "outputs": [],
-   "source": []
+   "source": [
+    "size = (160, 180)\n",
+    "\n",
+    "canvas = Canvas(size=size)\n",
+    "\n",
+    "# Possible line_cap values\n",
+    "line_caps = ['butt', 'round', 'square']\n",
+    "\n",
+    "# Draw guides\n",
+    "canvas.stroke_style = '#09f'\n",
+    "canvas.begin_path()\n",
+    "canvas.move_to(10, 30)\n",
+    "canvas.line_to(140, 30)\n",
+    "canvas.move_to(10, 140)\n",
+    "canvas.line_to(140, 140)\n",
+    "canvas.stroke()\n",
+    "\n",
+    "# Draw lines\n",
+    "canvas.stroke_style = 'black'\n",
+    "canvas.font = '15px serif'\n",
+    "for i in range(len(line_caps)):\n",
+    "    line_cap = line_caps[i]\n",
+    "    x = 25 + i * 50\n",
+    "\n",
+    "    canvas.fill_text(line_cap, x - 15, 15)\n",
+    "    canvas.line_width = 15\n",
+    "    canvas.line_cap = line_cap\n",
+    "    canvas.begin_path()\n",
+    "    canvas.move_to(x, 30)\n",
+    "    canvas.line_to(x, 140)\n",
+    "    canvas.stroke()\n",
+    "\n",
+    "canvas"
+   ]
   }
  ],
  "metadata": {

ipycanvas/canvas.py

@@ -77,6 +77,9 @@ class Canvas(DOMWidget):
     #: (float) Sets the width of lines drawn in the future, must be a positive number. Default to ``1.0``.
     line_width = Float(1.0)
 
+    #: (str) Sets the appearance of the ends of lines.
+    line_cap = Enum(['butt', 'round', 'square'], default_value='butt')
+
     def __init__(self, *args, **kwargs):
         """Create a Canvas widget."""
         #: Whether commands should be cached or not
@@ -272,7 +275,7 @@ def flush(self):
 
     @observe('fill_style', 'stroke_style', 'global_alpha', 'font', 'text_align',
              'text_baseline', 'direction', 'global_composite_operation',
-             'line_width')
+             'line_width', 'line_cap')
     def _on_set_attr(self, change):
         command = {
             'name': 'set',